Keeping food and drink fresh is a significant challenge for the packaging industry. Most common packaging materials are very poor at stopping gas transfer into and out of packaged food. Over the last thirty years an industry has developed in providing barrier film layers. These films are used to stop the transfer of gases such as water vapour, O2, CO2 and N2 into and out of food & beverages. Plastic has been used as a packaging material for over sixty years and is continuing to evolve through increasing demands from the market and through technical developments. One important requirement of many plastic packages is to keep food and drink fresh. The greatest cause of spoilage in food and drink is oxygen infiltration leading to oxidation.
The commodity plastics such as polyethylene terephthalate (PET), polypropylene (PP), polyvinyl chloride (PVC) and polyethylene (PE) all have some barrier to O2 and H2O. This barrier is proportional to the thickness of the barrier layer. Three factors drive the need for higher barrier performance plastics, firstly the move away from glass and tin/aluminium because of their weight, cost and breakability, secondly the down gauging of plastic materials to make them more economic and thirdly the requirement for extended shelf life as more food is packaged into ever smaller servings sizes. This has led to the development of materials that significantly enhance the barrier properties of common consumer plastic packaging.
The first successful high performance barrier material was polyvinylidene chloride (PVDC). It is a derivative of PVC and therefore is seen to have a similar negative environmental profile.
The other common barrier materials on the market today are ethylene vinyl alcohol copolymer (EVOH), nylons (e.g. MXD6) and nitrites. These are all used as a barrier layer to the structural layer provided by the commodity plastics.
The only natural polymer that has been commercialized that can be used as a barrier material is cellophane which was developed well before much of the plastics industry. Its barrier properties to oxygen are not considered high performance compared to today's barrier resins and its cost is high.
A common barrier structure of the wall of PET (polyethylene terephthalate) drink bottles is a multi-layer structure consisting of PET structural layers around a core layer or layers containing higher-priced barrier materials.
U.S. Pat. Nos. 5,498,662, 562,102, 65,897,960 and 6,143,384 disclose the use of polymethacrylic acid polymer and polysaccharides in barrier layers.
WO 00/49072 discloses barrier coatings based on clays such as montmorillonite spray coated onto PET blow moulded bottles.
USA application 2004/0087696 discloses a water based coating for PET containers in which a clay material is mixed with a melamine, formaldehyde and boric acid binder and an organic water soluble binder such as polysaccharides and cellulose materials.
Barrier materials are used in a host of different plastic structures and processes and each of these imposes its own functionality requirements. The most common use of barrier structures is in thin films for wrapping foods such as confectionery, bakery products and the plethora of pouches appearing in the market over the last five years. Some of these films can have 12 layers and yet be less than 50 μm thick. These films are typically produced through co extrusion.
WO 90/14938 discloses a high amylose modified starch that is suitable for use in oxygen barrier laminates.
U.S. Pat. Nos. 6,569,539 and 6,692,801 disclose a paper and or plastic laminate with an inner barrier coating of a starch or modified starch applied from a dispersion.
WO04/052646 discloses a multilayer barrier film using a starch layer and a biodegradable polyester layer.
USA application 2002/0187340 discloses a gas barrier coating of polyvinyl alcohol and starch in which the predominant material is starch and the material is applied from a dispersion.
Barriers are also used in bottles for fruit juice, in some carbonated soft drinks and in various hot filled foods such as fruit and vegetable preserves. Bottles are usually formed through co-injection stretch blow moulding. This requires the materials to be both injection moulded into a preform and then remelted and blown into a bottle shape. Other containers may be co-extrusion blow moulded, where the parison is blown against a mould wall to achieve the desired shape online during the co-extrusion process.
Some containers furthermore require high-gas-barrier closures, formed by means of injection moulding.
The other significant area of use of barrier materials is in rigid packages such as meat trays although for most applications the rigid plastic material provides enough barrier and only the thin film on top needs improved performance.
One issue that is seen to hold back the rollout of barrier technologies is their effect on the recyclability of the plastic—this is particularly true for the bottle market.
Many PET bottles now have a complex structure of virgin material on the exterior with recycled PET and barrier layers in the middle. If the barrier resin is not compatible with the recycling system then there is a large resistance to moving towards that technology.
Finally, new materials are entering the market, that are based on sustainable, renewable resources and/or that are biodegradable. An example of such a material that may be injection stretch blow moulded into bottles or formed into thin films for packaging applications is polylactic acid synthesised from corn. PLA is a poor gas barrier and also a relatively poor water vapour barrier and in order to preserve biodegradability or sustainability status would benefit from a biodegradable barrier based on renewable resources.
It is an object of this invention to provide a barrier film that is less expensive than prior art materials and is easy to laminate with existing packaging materials that can address the issues identified above.